1. Field of the Invention
The present invention relates to a rotary connector accommodating a cable used for transmitting electric signals, optical signals, etc. between a rotary body and a fixed body.
2. Description of the Related Art
One method proposed for laying a cable which is used for supplying power or transmitting signals through a rotary portion such as the steering wheel of a car has been for example to connect one cable to an inside case of a rotary connector of a rotatable structure and connect another cable to the outside case. The inside case and the outside case are rotatable with respect to each other and a cable is provided between the inside case and outside case for intermediate connection.
In the past, the intermediate connection cable of a rotary connector would strike the inside of the rotary connector when vibration occurred. The noise caused by this was disturbing and prompted measures to be taken against it. Further, measures have been taken to prevent the intermediate connection cable from becoming loose between the inside case and outside case or from being subjected to excessive tension.
Such a rotary connector of the related art will be explained in more detail here with reference to FIG. 1 and FIG. 2. FIG. 1 is a lateral sectional view of a rotary connector of the related art, while FIG. 2 is a sectional view along the line D--D of the same. In this rotary connector, the inside case 1 and outside case 2 are arranged to be rotatable relative to each other. A flat cable 3 is accommodated in the space formed between the inside case 1 and the outside case 2 in a spiral fashion. One end of the flat cable 3 is fixed to the inside case 1, while the other end is fixed to the outside case 2. Note that in the space formed between the inside case 1 and the outside case 2, there is a U-shaped turnback portion 3A comprised of the flat cable turned back in a U-shape. In the space 4 formed by this turnback portion 3A, a plurality of annular belts 5 are arranged.
Explaining how this rotary connector is used, for example, the inside case 1 is turned so as to wind the part of the flat cable 3 wound against the outside case 2 on the inside case 1 or wind the part of the flat cable 3 wound on the inside case 1 at the outside case 2 (rewind from the inside case 1). The plurality of annular belts 5 arranged in the space 4 formed by the turnback portion 3A of the flat cable 3 bias the part of the flat cable 3 wound on the inside case 1 and the part of the flat cable 3 wound against the outside case 2 away from the belts so as to prevent the part of the flat cable 3 wound on the inside case 1 and the part of the flat cable 3 wound against the outside case 2 from becoming loose and to enable smooth winding and rewinding of the flat cable 3.
In the above-mentioned rotary connector, however, when the inside case 1 is turned in an X-direction (counterclockwise direction) as shown in FIG. 1, since the directions of rotation of the adjoining annular belts 5 biasing the part of the flat cable 3 wound on the inside case 1 and the part of the flat cable 3 wound against the outside case 2 away from the belts are the same, the directions of rotation of the annular belts 5 where they contact each other end up becoming opposite from each other. Therefore, since each of the annular belts 5 are moved to the direction of the rotation of the inside case 1, the rotational torque becomes large and smooth rotation is no longer possible. Note that a similar problem occurs also in a case where the inside case 1 is turned in the clockwise direction.